Biofilm thickness effect on the diffusion limitation in the bioprocess reaction: Biofloc critical diameter significance

A convenient physical model for biomass involves consideration of individual cells as active centers dispersed through a continuous region in which transport takes place by molecular diffusion. This paper investigates for steady state conditions the variation of apparent kinetic constant (K_m) of bacteria in relation to biofloc diameter with solid and/or liquid-phase diffusion. When the biochemical reactions are limited only by liquid-phase diffusion, theK_m increases whenD increases. With solid-phase diffusion limitation only, theK_m increases linearly with the diameterD of the floc. When both solid and liquid-phase diffusion limitations are considered, the apparentK_m is affected by liquid-phase diffusion limitation with very smallD and by solid-phase diffusion limitation with higherD. The critical diameterD_c can be assumed to be theD at which solid-phase diffusion limitation becomes more significant than liquid-phase diffusion limitation.